Hydroxynitriles as flotation modifiers



rpm-ma United States Patent HYDROXYNITRILES AS FLOTATION MODIFIERS Erwin L. Carpenter and Robert B. Booth, Stamford, Conn., assignors to American Cyanamid Company, New York, N.Y., a corporation of Maine No Drawing. Filed Jan. 22, 1957, Ser. No. 635,135

Claims. (Cl. 209-167) This invention relates to improved flotation processes for mixed ores which contain several metallic values and require selective separations of their mineral components.

Mixed ores, such as lead-zinc ores, iron-bearing leadzinc ores, copper-zinc ores, copper-iron ores, complex copper-lea'd-zinc ores and the like, present problems of selective separations. Differential flotation processes have been developed in which one or more of the minerals, usually zinc and/ or iron, are depressed so that a concentrate of the remaining metal or metals can be obtained, whereupon the zinc can be reactivated with reagents such as copper sulfate and the like and then floated as a concentrate. The standard depressant is sodium cyanide, and with many ores excellent results can be obtained, provided a sulficient and controlled amount of sodium cyanide is used.

Commercially useful as the selective flotation processes using sodium or other soluble cyanides have proven to be, they are by no means perfect. For one thing the cost of cyanide adds to the processing cost and further, with some ores, the completeness of the selective depression is not as perfect as could be desired. This latter factor is of considerable importance especially when the mineral to be depressed is present in fairly large concentration or at least in concentration comparable to that of the desired mineral. Also in the latter case with lean ores, it is difficult to obtain high-grade concentrates. Contamination of each concentrate with other minerals is, therefore, still a problem which varies in seriousness from ore to ore.

According to the present invention, certain organic nitriles, namely alpha-hydroxynitriles, have been found to give results as depressants which are as good as sodium cyanide; in many cases better; and which, in the depression of certain minerals, such as iron minerals, can be used in smaller quantities than is practical with sodium cyanide. While the invention is not limited to any particular alpha-hydroxynitrile, we have found that lactonitrile, and particularly crude lactonitrile, is extremely effective. The latter, which is obtainable as a brownish black liquid by-product in the manufacture of acrylonitrile, can be obtained at a very low price. It is an advantage of the present invention that there is no significant difference between a pure alpha-hydroxynitrile and crude material such as the very dirty, crude lactonitrile referred to above. Why the extensive impurities, amounting to and more in the case of the crude lactonitrile, do not interfere with its depressant action is not known, but the possibility of using very crude and dirty material is a distinct advantage of the present invention and such crude by-product material constitutes the preferred reagents to be used.

The alpha-hydroxynitriles are organic liquids and thus can be fed readily either directly or in water solutions to conditioning or flotation operations. With the solid depressants formerly used, solution is an unavoidable 2,984,354- Patented May 16, 1961 The exact mechanism of the depressing action of the alpha-hydroxynitriles is not fully known. It is not merely a question of the presence of a CN group because prerequisite for uniformity of feeding. This added flexibility is an advantage of the present invention.

other nitriles, even other hydroxynitriles, either have no depressing action whatever or depress so slightly as to be of no commercial significance. We are therefore not dealing purely with a question of using any compound which has a CN group.

In the well-known selective flotation processes using various soluble cyanides of inorganic nature, it is customary to rate consumption on the basis of sodium cyanide equivalent; that is, the weight of a particular cyanide used which has the same weight of cyanide as a given standard weight ofsodium cyanide. Through; out the present specification this conventional nomenclature will be used. It is an advantage of the present invention that the froth flotation processes are in no way changed by using the alpha-hydroxynitriles of the present invention. The same techniques can be employed as have been used in the past with sodium cyanide as a depressant. It is therefore unnecessary for the practical operating man to learn any new techniques. These flotation conditions will vary, of course, from ore to ore, each ore having optimum requirements for the type and amount of flotation promoter used, frother, flotation time, pH, etc., and in the following illustrative examples in each case the flotation conditions will be used which have been found to be optimum for the operation when sodium cyanide is used. All examples are carried out in laboratory-type Fagergren flotation machine using 600 g. charges at standard flotation pulp density of about 25% solids. The standard laboratory procedure. used in the examples is highly reliable and is applicable to plant practice.

Example 1 The tests in this example were carried out with pyrite only to show relative depressing powers with different amounts of reagent.

A 90-10 silica-pyrite mixture was ground to 65 mesh with l lb./ton of lime and successive portions after dilution to flotation pulp density were floated in a Fagergren flotation machine at a pH of 9 with 0.1 lb./ton sodium ethyl xanthate as the promoter and 0.03 lb./ton polypropylene glycol as the frother. The flotation was effected for five minutes and the percentage of pyrite depressed determined. Varying amounts of sodium cyanide and lactonitrile were used in the different tests and one was run as a blank with the addition of no depressant. The results appear in the following table.

NaCN Lactonitrile It will be noted that the lactonitrile is a very much more active depressant for pyrite than is sodium cyanide. At 0.01 lb./ton NaCN equivalent there was no depression with sodium cyanide and quite substantial depression with lactonitrile which reached at an amount (0.015 lbL/ton) in which the NaCN gave no significantly useful results. More than twice as much NaCN had to be added before comparable depressions were obtained.

3 Example 2 Percent yrrhotite de ressed LbJton N aCN equiv. p p

NaCN Lactonitrile It will be noticed that lactonitrile showed very substantial depression in concentrations where sodium cyanide had no effectiveness at all and even at fairly high concentrations, the results were significantly better with the crude lactonitrile.

Example 3 This example used a test ore which is the same as in Example 1, the flotation being eifected at 22% solids. On successive portions diiferent nitriles were used and the results appear in the following table.

Compound tested as depressant:

Percentage of pyrite depressed It 'will be noted that most nitriles showed either no depression at all or a negligible amount, whereas the a'lpha-hydroxynitriles gave excellent depression. A particularly significant comparison is between ethylene cyanohydrin and lactonitrile, the latter being almost sixteen times as effective.

Example 4 A Missouri lead-zinc ore containing a small amount of pyrite and carbonate gangue minerals was ground to 65 mesh, diluted to about solids, conditioned for two minutes with 0.12 lb./ton sodium silicate and for three minutes longer with 0.09 lb./ton of sodium cyanide, followed by another two minutes with 0.03 lb./ton sodium ethyl xanthate and for one minute longer with a 0.12 lb./ton pine oil. The mixture was then floated for four minutes to obtain a lead concentrate.

The resulting tailing was conditioned for two minutes with 0.43 lb./ton soda ash and for a further four minutes with 1.0 lb./ton copper sulfate pentahydrate, followed by two minutes longer with 0.2 lb./ton technical sodium diethyldithiophosphate and for one minute longer with 0.07 lb./ton pine oil. The flotation was then carried on 'for four minutes to produce a zinc concentrate.

The procedure above was repeated, replacing the sodium cyanide with an equivalent amount of lactonitrile, and a third test was run again under the same conditions but with no depressant at all. The metallurgical results appear in the following table.

Depressant used NaCN Lacto- None nitrile Lead concentrate:

Assay, percent Pb 50. 8 57. 3 44. 4 Assay, percent ZN 3. 2 2. 2 3.8 Recovery, percent P 88. 0 88. 2 89. 5 1. 0 0.6 1. 3

Zinc concentrate:

Assay, percent Zn 53. 3 55.1 53.1 Assay, percent Pb.. 0.2 0.3 0. 2 Recovery, percent Z 97. 3 98. 1 95. 2 Recovery, percent Pb. 3. 5 1. 8 1.1

It will be apparent that while substantial depression was effected with sodium cyanide, the results with lactonitrile were definitely better; and in the lead concentrate, the lead was recovered with only 0.6 as much overall zinc contaminant. Similarly, the lactonitrile permitted a slightly better recovery of zinc in the zinc concentrate with only about half as much lead.

Example 5 A pyrite-bearing lead-zinc ore from northern New York analyzing 0.35% Pb, 9.1% Zn and 9.3% Fe was ground to mesh at 65% solids, diluted to about 22% solids, conditioned with 0.06 lb./ton sodium cyanide for three minutes and for two minutes longer with 0.06 lb./ton technical dicresyldithiophosphoric acid containing about 6% diphenyl thiourea. The pulp was then floated for four minutes to produce a lead concentrate, the pH being 7.4.

The tailings were then conditioned for two minutes with 4.0 lb./ ton of lime to produce a pH of 10.9, then for three minutes longer with 1.3 lb./ton copper sulfate pentahydrate, followed by two minutes with 0.13 lb./ton sodium ethyl xanthate and one minute with 0.16 lb./ton pine oil as a frother. Flotation as in the preceding examples was for four minutes to produce a zinc concentrate.

The procedure was repeated twice with equivalent amounts of lactonitrile and of acetone cyanohydrin in place of the sodium cyanide. The lactonitrile was a byproduct from the manufacture of acrylonitrile and contained about 85% of lactonitrile, the product being dirty and brownish black in color. Finally a control float was made under the same conditions with no depressant. The results of the tests appear in the following table.

It will be noted that a substantially better grade lead concentrate was obtained with the nitriles than with sodium cyanide and it was contaminated with less zinc. Recoveries were also somewhat better. In the case of the zinc concentrate again the grade was a little better 0 for the nitriles and the contamination with iron somewhat less.

Example 6' mesh with 1.0 lb./ton of sodium cyanide, 1.0 lb./ton zinc hydrosulfite, 1.0 lb./ton lime and 0.04 lb./ton of a 1:1 mixture of sodium mercaptobenzothiazole and sodium di(secondary butyl)dithiophosphate. After conditioning, the mixture was diluted to 20% solids and conditioned with 0.02 lb./ton of ammonium dicresyldithiophosphate and 0.02 lb./ton pine oil. Flotation was for three minutes to remove a lead concentrate which was cleaned by refloating with a 0.25 lb./ton zinc hydrosulfite and 0.25 lb./ton sodium cyanide.

The tailings from the lead rougher flotation operation were conditioned for five minutes with 2.0 lb./ton lime, 1.5 lb./ton copper sulfate penthahydrate and 0.1 lb./ton of a 1:1 mixture of sodium mercaptobenzothiazole and sodium di(secondary butyl)dithiophosphate. Thereupon the mixture was floated to remove a zinc concentrate which was cleaned by refioating with 0.5 lb./ ton lime and 0.05 lb./ton of the mercaptobenzothiazole-dithiophosphate mixture together with 0.04 lb./ton of pine oil as a frother.

A second test was run substituting an equivalent amount of crude lactonitrile for the sodium cyanide. The results appear in the following table.

Depressant used NaCN Lactonitrile Lead concentrate:

Assay, Percent Pb Assay, Percent Zn. Assay, Percent Fe Recovery, Percent Pb..-" Recovery, Percent Zn Zinc concentrate:

Assay, Percent Zn Assay, Percent Pb Assay, Percent Fe Recovery, Percent Zn.-. Recovery, Percent Pb (D O s s r ss (D OI mews:-

Example 7 An iron-bearing copper ore from Utah containing 0.9% Cu and 2.3% iron was ground to 60% solids 65 mesh with 2.6 lb./ton lime and 0.3 lb./ton sodium cyanide. The mixture was then diluted to 22% solids, conditioned for a minute with 0.03 1b./ton technical dicresyldithiophosphoric acid as promoter and then for one minute with 0.2 lb./ton of a 1:1 cresylic acid-fuel oil mixture as a frothing agent. Flotation was for five minutes to remove a copper concentrate.

The test was repeated, substituting by-product lactonitrile in equivalent amount for the sodium cyanide. The results of the tests appear in the following table.

It will be noted that the lactonitrile. gave slightly higher assay of copper with a somewhat increased recovery. This test illustrates that the nitriles are fully as good depressants as sodium cyanide, even on an ore which is specially suited for sodium cyanide repressant. As has been pointedout above, the improvements: obtained with the nitriles will vary from ore to ore.

We claim:

1. A method of selective froth flotation of ores containing depressable minerals selected from the group of zinc and iron minerals which comprises efiecting flotation in the presence of an effective amount of an alpha-hydroxynitrile selected from the group consisting of acetone,

cyanohydrin and those represented by the formula wherein R is selected from the group consisting of hydrogen, methyl and phenyl to produce a concentrate of the lead or copper relatively poor in zinc minerals, subjecting the tailings of the flotation operation to activation of the zinc minerals, refloating to produce a zinc concentrate relatively high in zinc and relatively low in lead or copper.

4. A flotation process according to claim 3 in which the ore is a lead-zinc ore.

5. A process according to claim 4 in which the alphahydroxynitrile is lactonitrile.

6. A process according to claim 3 in which the alphahydroxynitrile is lactonitrile.

7. A process according to claim 3 in which the ore is a copper-iron ore.

8. A process according to claim 7 in which the alphahydroxynitrile is lactonitrile.

9. A process according to claim 4 in which the nitrile is acetone cyanohydrin.

10. A process according to claim I in which the nitrile is acetone cyanohydrin.

References Cited in the file of this patent UNITED STATES PATENTS 1,552,936 McArthur Sept. 8, 1925 FOREIGN PATENTS 362,961 Great Britain Dec. 3, 1931 OTHER REFERENCES Taggart: Elements of Ore Dressing, John Wiley and Sons, Incorporated, 1951, pages 271-276.

Migrdichian: The Chemistry of Organic Cyanogen Compounds," ACS Monograph 105, Reinhold, New York, 1947, pages 173-176. 

1. A METHOD OF SELECTIVE FROTH FLOTATION OF ORES CONTAINING DEPRESSABLE MINERALS SELECTED FROM THE GROUP OF ZINC AND IRON MINERALS WHICH COMPRISES EFFECTING FLOATING IN THE PRESENCE OF AN EFFECTIVE AMOUNT OF AN ALPHA-HYDROXYNITRILE SELECTED FROM THE GROUP CONSISTING OF OCETONE CYANOHYDRIN AND THOSE REPRESENTED BY THE FORMULA 